A moisture-permeable material which comprises a porous base, e.g., a fabric, having a substantially non-porous layer of a hydrophilic polyurethane resin on a surface thereof and which is suitable for use as a material for garments, etc. is known. The layer of a hydrophilic polyurethane resin absorbs moisture from the high-humidity side and releases moisture to the low-humidity side. The layer thus functions to transmit moisture.
The main raw materials for the layer of a hydrophilic polyurethane resin comprise a polyol having high hydrophilicity and an isocyanate compound. In many cases, a two-pack type coating agent composition comprising a combination of an isocyanate-group-containing prepolymer obtained by reacting a polyol having high hydrophilicity with an isocyanate compound and a curing agent is used for forming the layer of a hydrophilic polyurethane resin.
Proposed as such coating agent compositions are: a coating agent composition forming a coating film or film which retains the flexibility and elongation of hydrophilic polyurethane resins in at least some degree and has high mechanical strength (patent document 1); a coating agent composition forming a coating film or film which has high elongation and high moisture permeability (patent document 2); and a coating agent composition which is satisfactory in mechanical properties such as tensile strength and abrasion properties, does not swell in water, and has satisfactory laundering durability (patented document 3).
However, the coating films obtained from the related-art coating agent compositions have a problem that they change in color to yellow by the action of sunlight or NOx because an aromatic polyisocyanate was used as a raw-material isocyanate compound for the isocyanate-group-containing prepolymer, that is, the coating films have poor yellowing resistance (light resistance and NOx resistance).
It is known that the yellowing resistance of a coating film to be obtained is improved by using an aliphatic polyisocyanate in place of the aromatic polyisocyanate.
However, since an aliphatic polyisocyanate brings about a low cohesive force, it is difficult to obtain a coating film which retains laundering durability and resistance to sweat deterioration. Resistance to sweat deterioration means resistance to the higher fatty acids, in particular oleic acid, which are a component of human sweat. In garment applications, coating films are desired to suffer neither swelling in nor deterioration by oleic acid and to have sufficient laundering durability. So far, an aromatic polyisocyanate has had to be used as a raw material for the isocyanate-group-containing prepolymer.
On the other hand, in the case where a catalyst is necessary for the reaction of a polyol with an isocyanate compound, an organotin compound (e.g., dibutyltin dilaurate) is used. In recent years, however, use of organotin compounds tends to be avoided because of growing concerns about environmental issues. Consequently, nonuse of an organotin compound is desired.
Patent Document 1: JP-A-62-57467
Patent Document 2: JP-A-3-229773
Patent Document 3: JP-A-2002-69370